Food packaging: reheating at exceedingly high temperatures increases the risk of substance migration

Changing dietary behaviour and consumption patterns have prompted industry to offer innovative solutions in the field of food packaging, in particular linked with nomadic lifestyles, the convenience of packaging or its environmental impact. In the framework of a research & development partnership agreement with the French National Consumer Institute, ANSES carried out a comparative study on food packaging that can be heated in conventional ovens, microwave ovens or by steam. The results of this study show that while the migration of substances from the packaging to the food is generally low and below the regulatory values, it can increase significantly in the case of non-compliance with instructions for reheating. To limit these risks of migration, ANSES therefore recommends carefully following the manufacturers' instructions in this regard.

The legislation puts responsibility for the safety of the processes used on the manufacturer, and also requires that specific instructions for safe and appropriate use be displayed on the food containers. To date, however, few data have been published in the scientific literature on the impact of different reheating practices on exposure of consumers to substances present in packaging materials. 

ANSES therefore carried out a study on this issue in partnership with the French National Consumer Institute. Several studies were carried out on different types of packaging (food bags for use in conventional or microwave ovens, bags for steaming or microwave ovens, and trays).

In the samples studied, regardless of the type of packaged food, polypropylene was found to be the polymer most often used.

In the framework of the study concerning polypropylene food trays designed to undergo cooking in conventional or microwave ovens, the tests conducted under three conditions (ambient temperature, heating in the microwave following the manufacturer’s recommendations, and extreme heating) revealed the presence of POSHs (which can potentially be used as lubricants) in several samples kept at ambient temperature. The level of POSH increased during reheating, and particularly in the case of extreme reheating (higher temperatures and for extended periods).

The Agency's recommendations

The results of this study lead the Agency to advise consumers to follow the manufacturers’ recommendations (degree and duration of cooking) indicated on the food packaging, as extreme reheating increases the risk of substance migration.

A few reminders about packaging and reheating techniques

To make the best use of a microwave oven, ANSES makes the following recommendations:

  • always check before use that the kitchenware is compatible with use in a microwave oven (this should be indicated by the manufacturer) and in good condition;
  • do not keep single-use packaging for use as containers for microwaving food (e.g. do not reuse a food tray);
  • prefer long reheating times but at low power (e.g. 2 minutes at 650W is preferable to 50 seconds at 1270W), especially if no specific instructions can be found on a food's packaging;
  • avoid the use of microwave ovens for reheating infants' feeding bottles: the distribution of temperatures obtained within the food could potentially cause burns to the child.

In addition, the Agency recommends avoiding the use of damaged packaging or packaging showing signs of wear.

As regards acidic foods (tomatoes, recipes using lemon juice, etc.), the Agency reiterates that consumers are strongly advised not to store or reheat such foods in aluminium foil, because the acidity increases the migration of aluminium into the food.